Process of preparing acrylonitrile and methacrylonitrile by catalytic ammoxidation of propylene and isobutylene



3,426,060 PROCESS OF PREPARING ACRYLONITRILE AND METHACRYLONITRILE BY CATA- LYTIC AMMOXIDATION OF PROPYLENE AND ISOBUTYLENE Jamal S. Eden, Akron, Ohio, assiguor to The B. F. GoodriKchkCompany, New York, N.Y., a corporation of New or No Drawing. Filed Aug. 30, 1965, Ser. No. 483,792 US. Cl. 260-465.? 14 Claims Int. Cl. C07c 121/02, 121/32 ABSTRACT OF THE DISCLOSURE Propylene or isobutylene is reacted with ammonia and oxygen at an elevated temperature in the presence of a catalyst containing molybdenum oxide, tellurium oxide and a bismuth or antimony phosphate to form acrylonitrile or methacrylonitrile.

This invention relates to a method of preparing acrylonitrile or methacrylonitrile by ammoxidation of monoolefinic hydrocarbons containing 3 to 4 carbon atoms at an elevated temperature, and relates more particularly to a method of preparing acrylonitrile or methacrylonitrile by passing vapors of propylene or isobutylene, ammonia and an oxygen containing gas at a temperature of from about 375 C. to about 500 C. over a catalyst comprising a mixture of a molybdenum oxide, tellurium oxide and a bismuth or antimony phosphate in a molar ratio of 100 M -100 TeO and 10-100 of a bismuth or antimony phosphate. The catalyst can also be designated as Mo Te M P O wherein M is OI P being in the form of a phosphate i.e. each P atom is attached to 3 to 4 oxygen atoms.

Nitriles have been prepared by ammoxidation of hydrocarbons, especially from the normally gaseous hydrocarbons. However, prior catalysts and procedures for ammoxidizing propylene or isobutylene to acrylonitrile or methacrylonitrile have certain shortcomings. The catalysts either have a very short active life, or they convert only a portion of the hydrocarbon to the desired unsaturated nitrile per pass; they oxidize the hydrocarbon excessively to form high proportions of carbon monoxide or carbon dioxide or both or they are not sufficiently selective, so that the hydrocarbon molecule is attached at both the olefinic unsaturation and at a methyl group and large amounts of HCN and acetonitrile are formed.

It is therefore unexpected to find a catalyst that will convert from over to as high as 100% per pass of a monoolefin containing 3 to 4 carbon atoms to yield very high proportions of acrylonitrile or methacrylonitrile. A further unexpected feature is the unusually long active life of the catalyst along with the concurrent production of acrylic acid in recoverable amounts.

THE REACTANTS The essential reactants are propylene or isobutylene, ammonia and an oxygen containing gas, which can be pure oxygen, oxygen enriched air or air Without additional oxygen. For reasons of economy, air is the preferred oxygen containing reactant.

The addition of steam into the reactor along with the monoolefin, ammonia and an oxygen containing gas is desirable but not absolutely essential. The function of steam is not clear, but it does seem to reduce the amount of carbon monoxide and dioxide in the eflluent gases.

Other diluent gases can be used. Surprisingly, saturated hydrocarbons such as propane or butane are rather inert under the reaction conditions. Nitrogen, argon, krypton or nited States Patent 0 3,426,060 Patented Feb. 4, 1969 other known inert gases can be used as diluents if desired but are not preferred because of the added cost.

THE CATALYST AND ITS PREPARATION There are several methods for the preparation of the catalyst, which can be supported or unsupported. It is possible to dissolve each of the starting ingredients in water and combine them from the aqueous solutions or the ingredients can be dry blended. Because of the more uniform blend obtained by the solution procedure, it is preferred.

The general procedure for preparing a catalyst from water soluble ingredients is to provide the requisite amount of a molybdenum salt, a tellurium salt and a bismuth or antimony salt in Water. Add the requisite amount of phosphoric acid to the Bi or Sb solution. Add the tellurium salt solution to the molybdenum salt solution and then add the bismuth or antimony salt-phosphoric acid mixture to the molybdenum-tellurium salt mixture. The catalyst is then dried and baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding an aqueous slurry of the support to the aqueous solution of catalyst or the aqueous catalyst ingredients can be added to the slurry of the support.

Alternately a slurry of the catalyst ingredients can be prepared in water, then dried and baked. For supported catalysts the aqueous slurry of the catalyst ingredients can be added to an aqueous suspension of the support or vice versa, and then dried and baked.

A third method is to blend the dry ingredients and then mix them thoroughly. The main difiiculty is to obtain thorough blending and uniform particle size.

A specific procedure for making the catalysts is as follows:

In this procedure the ingredients are precipitated on blending.

(a) Dissolve 105.9 6 g. of ammonium molybdate in 130 ml. of water at about 50 C.

(b) Dissolve 31.922 g. TeO in concentrated HCl and filter if necessary.

Add the tellurium salt solution to the ammonium molybdate solution. A precipitate forms.

(c) Dissolve 133.4 g. of BiCl in water and add 46.2 g. of H PO Add this mixture slowly to the precipitated ammonium molybdate-Te0 mixture.

Dry the mixture on a steam bath and bake for 16 hours at 400 C. Thereafter the catalyst is ground to the desired mesh size and sieved. For supported catalysts an aqueous slurry of the support can be added to the catalyst ingredients or vice versa prior to drying and baking. Empirically this catalyst iS MO1 T63 33Bl5 P 5 O5 3.33 and P is present as phosphate P0 Among the suitable supports are silica, silica containing materials such as diatomaceous earth and kieselguhr, silicon canbide, clay, aluminum oxides and even carbon, although the latter tends to be consumed during the reaction.

If the catalyst is to be supported the aqueous solution of ingredients can be added to an aqueous slurry of the support or vice versa, prior to drying. The procedure after drying is the same as that already described. Thus, to the aqueous catalyst ingredients 240 g. (1.2 mols) of a 30- 35% aqueous collodial dispersion of microspheroidal silica (Ludox HS.) are added slowly with stirring. Stirring is continued for about /2 hour prior to drying. Another procedure is to add the mixture described under (c) to the Ludox and then add the requisite amount of TEO and M00 as a slurry. Also the ingredients can be added to the Ludox individually if desired.

Another method is to grind M00 TeO and a bismuth phosphate to the proper :particle size and then thoroughly mix the dry powders. The mixture can be added to an aqueous slurry of a support or vice versa and thereafter dried and baked.

For fixed bed systems a 1018 mesh (U.S. Sieve) size is satisfactory. For fluid bed systems the catalyst particle size should be 80-325 mesh (U.S. Sieve).

The exact chemical structure of the catalysts made by the above procedures is not known, but catalysts with molar ratios of 100 Mo, 10-100 Te and 10-100 of a bismuth or antimony phosphate can be used for ammoxidizing the monoolefinic hydrocarbon to the nitriles. The catalyst contains chemically bound oxygen so that the generic formula can be written as 3 o 2 10-100 BiPO4 1o 100 The phosphate can be a Fo radical, pyrophosphate or a polyphosphate.

REACTION CONDITIONS The reaction can be carried out in either a fixed or fluidized catalyst bed.

The reaction temperature can range from about 375 to 500 C. but the preferred range is from about 400 to about 480 C. Below about 375 C. the conversion of monoolefin per pass and yield of unsaturated nitrile is lower than desirable. Usually, a longer contact time is needed at lower temperatures to obtain the yields of unsaturated nitriles obtainable at temperatures in the opti mum range.

Above 480 C. some of the acrylonitrile appears to be oxidized to carbon oxides, acetonitrile and HCN. This is much more apparent at 500 C.

The mol ratio of oxygen to propylene should be from 1.5 to 1 and preferably from 2 to 1 to 4 to 1 for good Care is needed to operate at a pressure which is below the dew point pressure of the acrylonitrile or methacrylonitrile at the reaction temperature.

The example is intended to illustrate the invention but not to limit it.

EXAMPLE I The bismuth-containing catalyst used in this example was prepared by the solution procedure described above. It contained a molar ratio of 75 M00 TeO and 50 BiPO and was unsupported. A high silica glass (Vycor) tube 12 inches long and mm. in outer diameter was filled with 170 ml. of the catalyst. Three external electrically operated heating coils were wound on the reactor. One of the coils extended along the entire length of the reactor and each of the remaining coils extended about one half the length of the reactor. Outlet vapors were passed through a short water cooled condenser. Uncondensed gases were passed through a gas chromatograph (Perkin-Elmer Model 154D) and analyzed continuously. The liquid condenser was weighed and then analyzed for its acrylonitrile content in the gas chromatograph.

Steam at a temperature of 200-250 C. was first passed into this fixed bed reactor. Then propylene and air were fed separately into the stream of water vapor. The mixture passed through a pre-heater and entered the reactor at a temperature of ZOO-250 C. The reactor was preheated to about 300 C. before the gas feed was begun. The molar ratio of the feed was 3 mols of oxygen (supplied as air) per mol of propylene. The mols of water per mol of propylene, mols of ammonia per mol of propylene and the temperature in the reactor and cold contact time are set forth in the table below. No acetonitrile could be detected in the effluent gases.

Contact time, Conversion, Yield, mol percent Run Water, mols NHs, mols Temperature, 0. seconds mol percent Acrylic Acid Acrylonitrile conversion and yields, but ratios with some excess oxygen, EXAMPLE 11 33 to 100% is even more desirable and is preferred. There is no critical upper limit as to the amount of oxygen, but when air is used as the oxygen containing gas it becomes apparent that too great an excess will require large reactors, pumping, compressing and other auxiliary equipment for any given amount of desired end product. It is therefore best to limit the amount of air to provide 33 to 66% excess of oxygen. This range provides the largest proportion of nitrile, under given reaction conditions. Also, since care is needed to avoid an explosive mixture the limiting of air aids in that direction. The mol ratio of ammonia to propylene can range from about 0.5 to 1 to about 1.75 to 1. The preferred ratio is 0.75 to 1.5 of ammonia per mol of propylene.

The molar ratio of steam to propylene can range from 0 to about 7, but best results are obtained with molar A catalyst was prepared as follows:

(a) Dissolve 105.96 g. of ammonium molybdate in 130 ml. distilled water.

(b) Dissolve 31.922 g. TeO in 80 ml. concentrated HCl and filter if necessary.

Add the tellurium salt solution to the ammonium molybdate solution. A precipitate forms.

(0) Dissolve 91.24 g. SbCl in water and add 69.2 g. of 85 H PO Add this mixture slowly to the precipitated ammonium molybdate-TeO mixture.

Dry on a steam bath and bake for 16 hours at 400 C. Thereafter, the catalyst is ground to 1018 mesh size and sieved.

This catalyst was used as described in Example I under the same reaction conditions except as set forth in the table below.

Contact Conversion Mol percent yield on Run H2O, Mols NH,3 Mols Temp., O. time mol percent Acrolein propylene converted secon 5 Acrylic Acid Acrylonitrile ratios of about 3 to 5 per mol of propylene and for this reason are preferred.

The contact time can very considerably in the range of about 2 to seconds. Best results are obtained in a range of about 8 to 54 seconds and this range is preferred.

The particle size of catalyst for fixed bed and fluid bed systems has already been described.

The reaction can be run at atmospheric pressure, in a partial vacuum or under induced pressure up to 50-100 p.s.i. Atmospheric pressure is preferred for fixed bed systems and a pressure of 1 to 50 psi. for fluid bed reactions.

The desired end products result from the ammoxida- 6 tion of only one methyl group on the hydrocarbon 6. A method of preparing acrylonitrile comprising passmolecule, while the terminal ing a mixture of about 3 mols of oxygen supplied as air, about 4 mols of water vapor and about 1.25-1.3 mols of CH2=O\ ammonia per mol of propylene through a bed of a cata- 5 lyst consisting essentially of a mixture of M00 Te0 group remains intact. and Sb (P O7) in a molar ratio of 75 M00 25 TeO' The nltrlles produced can be defined as p beta and 50 511 0307 at a temperature of about 440 c.

monoolefinically unsaturated nitriles having 3 to 4 card a ld t t time of about 38 seconds. bon atoms and a terminal 7. Amethod of preparing acrylonitrile comprising pass- 1O ing a mixture of about 3 mols of oxygen supplied as air, about 4 mols of Water vapor and about 1.25-1.3

mols of ammonia per mol of propylene through a bed of group or they can be defined the genoral formula a catalyst consisting essentially of a mixture of M00 H Te=O and MP0,; in a molar ratio of 75 M00 25 T602 (CHEM and 50 BiPO at a temperature of about 440 C. and a CHFC-CN cold contact time of about 38 seconds. I claim; 8. The method of claim 1 in vwhich the catalyst is in a 1. A method of producing compounds of the formula fixed 9. The method of claim 1 in Wind] the catalyst 1s 1m- HutH pregnated on a silicic support.

' 10. A method of preparing methacrylonitrile compris- CH2=C CN ing passing a mixture containing a molar ratio of one comprising, passing a mixture of a molecular oxygen mol of tsobutylchc, a molecular oxygen containing gas in containing gas in a quantity sufficient to provide a molar a q y Sufllclcht to p f from about 2 to about 4 ratio of from about 1.5 to about 4 mols of oxygen per mols of oxygen P mol of lsooutylcuc, P to 5 mols of l f a hydrocarbon f h f ul water vapor and from 1 to 1.75 mols of ammonia per mol of isobutylene, through a catalyst consisting essentially (EHQH of a mixture of M00 TeO and an antimony or bismuth phosphate in a molar ratio of 100 M00 10- 100 TeO and 10-100 of phosphate at a temperature of from one mol of said hydrocarbon, and from about 0.5 to 1.75 about fllld a Contact time of from about mols of ammonia per mol of said hydrocarbon, over a 2 to about 70 Secondscatalyst consisting essentially of a mixture of molybde- Thc method of claim 10 in Which the catalyst has num oxide, tellurium oxide and a bismuth or antimony molar ratio of 75 3, 25 z and 4( 2 7)3- phosphate in a molar ratio of 100 molybdenum oxide, Thc t of claim 10 in Which thc c y has 10-100 tellurium oxide and 10-100 of antimony or bisa molar fatlo of 109 3, 25 z and 4 uth phosphate t a temperature f f about 375 t 13. The method of claim 3 where the catalyst contains about 500 C. at a contact time of from about 2 to a major Proportion of 3 and lesser Proportions of seconds. TeO and BiPO 2, Th th d f l i 1 i hi h th hydrocarbon 4O 14. The method of claim 3 where the catalyst contains is propylene and the temperature ranges from about 400 a major Proportion of s lesser Proportions of to about 480 C. to thereby produce acrylonitrile. 2 and h 2 03- 3. A method of preparing acrylonitrile comprising passing a mixture containing a molar ratio of one mol of References Clted propylene, sufiicient molecular oxygen containing gas 45 UNIT D TAT PATENTS to provlde from about 2 to about 4 mols of oxygen per 3,200,141 8/1965 Milberger 260M653 mol of propylene, from up t about 7 111015 of Water 3,226,421 12/1965 Giordano et a1. 260465.3 vapor per mol of propylene and from about 1 to about 1.5 mols of ammonia per mol of propylene over a catalyst FOREIGN PATENTS consisting essentially of a mixture of M00 TeO and a 50 9 9 8/1963 Great Britain bismuth or antimony phosphate in a molar ratio of 100 M00 10-100 TeO and 10-100 bismuth or antimony OTHER REFERENCES phosphate at a temperature of from about 400 to about Kogyo, tDerwent Belgian, Report No. 66A 7/15/1960, 480 C. 'with a contact time of 2 to 54 seconds. p. A-23.

4. The method of claim 3 in which the catalyst has a 5r molar ratio of about M00 25 TeO and 50- Sb a JOSEPH Exammer' 2 7)a- 5. The method of claim 3 in which the catalyst has a molar ratio of 75 M00 25 TeO and 50 BiPO 252434, 604 

